1. Field of the Invention
The present invention relates to a light emitting device and a light emitting element, and in particular, to a light emitting device from which light that has been emitted from a light emitting element can be efficiently taken out, and a light emitting element.
2. Description of the Related Art
A conventional method for manufacturing an LED (light emitting diode) element by growing a semiconductor crystal made of a group III nitride based compound semiconductor on a base substrate, such as sapphire, is known A problem arises in such an LED element, where light that has been generated in a light emitting layer is confined in a layer having a high optical absorption coefficient or absorbed within the layer, and thereby, the efficiency of radiation to the outside is lowered.
In order to solve this problem, unevenness is provided to the surface of some types of LED elements, so as to increase the efficiency of taking out light (see, for example, Japanese Patent Application Laid-Open No. 2003-69073 (FIG. 1, [0011])).
In the LED element that is described in Japanese Patent Application Laid-Open No. 2003-69075 (FIG. 1, [0011]) a gallium nitride based compound semiconductor layer (hereinafter referred to as GaN based semiconductor layer) is layered on a sapphire substrate so as to form a GaN substrate, and subsequently, other GaN based semiconductor layers are layered sequentially on top of this. The sapphire substrate is removed from this layered body, and etching is carried out on the rear surface (surface opposite to the surface on which the element is layered) of the GaN substrate, and thereby, a pit in step form is formed.
In the LED element that is described in Japanese Patent Application Laid-Open No. 2003-69075 (FIG. 1, [0011]), the rear surface of the GaN substrate has a specific form where a pit in step form has been created, and therefore, light can be effectively taken to the outside, by preventing light interference caused by multiple reflection within the GaN based semiconductor layers.
In the LED element that is described in Japanese Patent Application Laid-Open No. 2003-69075 (FIG. 1, [0011]), however, ability to take out light that has been confined within a GaN based semiconductor layer (light confined within a layer) depend on a difference in the refractive index vis-á-vis the sealing member around the element, and a sufficient ability to take out light cannot be gained in a state where a reflection from the interface occurs on the basis of the difference in the refractive index vis-á-vis the sealing member, even in the case where unevenness processing has been carried out on the surface of the element. In addition, though an increase in the efficiency of taking out light car be achieved by scattering light that has been confined within a GaN based semiconductor layer, this is not an ideal form or anything close to this. A problem also arises concerning this light that is confined within a layer, where the amount of light is reduced when it propagates over a long distance within a layer having a large optical absorption coefficient so as to attenuate, and in addition, the amount of generated heat increases within the element.
Accordingly, an object of the present invention is to provide a light emitting device from which light that has been emitted from a light emitting element can be efficiently taken out, and a light emitting element.